Field of the Invention
The present invention relates to a system for monitoring an operation of an ATM (Asynchronous Transmission Mode) cross-connecting apparatus, and an ATM cross-connecting apparatus having a function of monitoring the operation of itself.
In an ATM communication network, information contained in a cell is transmitted through an ATM cross-connecting apparatus provided in each node of the ATM communication network. Each ATM cell contains a virtual path identifier (VPI) assigned to each virtual path, where, generally, a plurality of virtual paths can be set in each link established between each two adjacent nodes in the network, and the virtual path identifier (VPI) is assigned to recognize each virtual path in each link. When an ATM cross-connecting apparatus inputs an ATM cell from one of a plurality of input ports thereof, the ATM cross-connecting apparatus converts (rewrites) a virtual path identifier in the ATM cell in accordance with a VPI conversion table provided in the ATM cross-connecting apparatus, and then the ATM cell is switched to an output port to be output therefrom, corresponding to the input port from which the ATM cell has come in, where the output port is determined in accordance with a routing table provided in the ATM cross-connecting apparatus. It is necessary to examine the normality of the functions of converting the virtual path identifier and switching the route of the ATM cell. The present invention relates to a system for monitoring the normality of the operations of the ATM cross-connecting apparatus, in particular, to a system for monitoring the normality of the VPI conversion table in the ATM cross-connecting apparatus.
The monitoring of the ATM cross-connecting apparatus is carried out by generating and inputting an OAM (Operation, Administration, and Management) cell, and monitoring the content of the ATM cell output from the ATM cross-connecting apparatus. FIG. 1 is a diagram illustrating a format of an OAM cell which is used for monitoring the operation of the ATM cross-connecting apparatus. In the example of FIG. 1, the ATM cross-connecting apparatus to be monitored is assumed to contain a switch unit of a capacity of 2.4 Gbps, for cross-connecting a plurality of input ports with a plurality of output ports, a plurality of input-side and output-side interface units, a plurality of first-stage multiplexers/demultiplexers of a capacity of 600 Mbps, and a second-stage multiplexer/demultiplexer of a capacity of 2.4 Gbps. The first and second-stage multiplexers/demultiplexers are provided between the switch unit and the plurality of input and output ports. The OAM cell in FIG. 4 contains a header portion of six bytes and an information field of 48 bytes. The two bytes from the top in the header portion are added in the ATM cross-connecting apparatus when the OAM cell is input therein, and the remaining 52 bytes correspond to the format of the usual ATM cells transmitted on transmission lines except that the HEC portion is deleted therefrom. In the format of FIG. 1, "OAM" denotes a two-bit identifier area which indicates that this ATM cell is an OAM cell, P1 denotes a two-bit area for identifying an output port from which a currently flowing ATM cell is to be output in each first-stage multiplexer/demultiplexer of 600 Mbps, P2 denotes a two-bit area for identifying an output port from which a currently flowing ATM cell in the second-stage multiplexer/demultiplexer of 2.4 Gbps, P3 denotes a four-bit area for identifying an output port from which an ATM cell currently flowing in the switch unit of 2.4 Gbps, is input thereto, and the other areas correspond to the well-known areas defined by the CCITT recommendation. For example, "VPI" denotes the above-mentioned virtual path identifier, "VCI" denotes a virtual channel identifier, "PT" denotes a payload type, "R" denotes a reserve field, and "C" denotes a cell loss priority. In the information field in the OAM cell used for monitoring the operation of the ATM cross-connecting apparatus, a PN pattern generated from a generator polynomial, for example, X.sup.11 +X.sup.2 +1. In the above switch unit, the cross-connecting is performed in accordance with the information in the area P3. In each of the above first-stage and second-stage multiplexers/demultiplexers, an output port from which each ATM cell is to be output is determined based on the contents in the above areas P1 and P2, respectively.
FIG. 2 is a diagram illustrating a sequence of monitoring the normality of an ATM cross-connecting apparatus by inputting an OAM cell for monitoring the operation of the ATM cross-connecting apparatus. Generally, a plurality of OAM cells for the monitoring are generated and input into the ATM cross-connecting apparatus through the plurality of input ports. Each OAM cell of the format of FIG. 1 is generated at an OAM cell generating point #i corresponding to each input port (i=1 to n, and n is the number of the input ports of the ATM cross-connecting apparatus) at a timing provided from a sequencer 101 to input the ATM cell into the ATM cross-connecting apparatus through a corresponding (i-th) input port. In addition to the above construction, a plurality of VPI conversion units each containing a VPI conversion table, are provided corresponding to the plurality of input ports. Further, a routing table is provided for setting therein information for determining the connection between the plurality of input ports and the plurality of output ports in the switch unit. Each VPI conversion unit converts a virtual path identifier contained in an ATM cell which is input from a corresponding input port, to another virtual path identifier for identifying a virtual path in the outgoing direction, through which the ATM cell is to be transmitted. For each of the plurality of input ports, one VPI conversion table as mentioned above is provided. Before the above input of the ATM cell, the contents of the VPI conversion tables and the routing table in the ATM cross-connecting apparatus are rewritten at a timing provided from a sequencer 111 in the ATM cross-connecting apparatus. When an ATM cell is input, the ATM cross-connecting apparatus rewrites the content of the area VPI for the virtual path identifier in accordance with the above-rewritten VPI conversion table, and outputs the ATM cell from an output port which is determined based on the above-rewritten routing table. At the OAM cell detecting point #j (j=1 to n) corresponding to each output port, the normality of the ATM cross-connecting apparatus is examined by determining whether or not the above content of the OAM cell output from the output port of the ATM cross-connecting apparatus as above coincides with the content of the OAM cell which is expected to be output from the output port when the ATM cross-connecting apparatus normally operates.
However, conventionally, as indicated in FIG. 3, the monitoring of the normality of the ATM cross-connecting apparatus is carried out for portions of each VPI conversion table which are not used for the conversion of the virtual path identifiers in ATM cells of the main signals (users' signals). Therefore, conventionally, other portions of each VPI conversion table which are used for the conversion of the virtual path identifiers when cross-connecting ATM cells of the main signals (users' signals), cannot be examined regarding their normality.